Nanoelectrospray ion generation for high-throughput mass spectrometry using a micromachined ultrasonic ejector array

Ultrasonic electrospray ionization (ESI) for high-throughput mass spectrometry is demonstrated using a silicon micromachined microarray. The device uses a micromachined ultrasonic atomizer operating in the 900 kHz-2.5 MHz range for droplet generation and a metal electrode in the fluid cavity for ionization. Since the atomization and ionization processes are separated, the ultrasonic ESI source shows the potential for operation at low voltages with a wide range of solvents in contrast with conventional capillary ESI technology. This is demonstrated using the ultrasonic ESI microarray to obtain the mass spectrum of a 10 μM reserpine sample on a time of flight mass spectrometer with 197:1 signal-to-noise ratio at an ionization potential of 200 V.